The title "Duke of Castile" refers to a noble rank historically associated with the region of Castile in Spain. This title was often granted to members of the royal family or high-ranking nobles, signifying their importance and influence in the region. The Dukes played a significant role in the political and social landscape of medieval Spain. The title has its roots in the Kingdom of Castile, which was a powerful kingdom during the Reconquista. The Dukes of Castile were involved in various military campaigns and governance, contributing to the unification of Spain. Over time, the title has become less prominent, but it remains a symbol of noble heritage.